You are confusing two completely separate things here…

The number of users that your product license covers has nothing at all to do with the number of simultaneous connections that your server allows. A 10 user product license allows up to 10 different users to be able to access WSE RemoteApp. However, out-of-the-box the Essentials server only allows two simultaneous connections with the server.

That being said, WSE RemoteApp has a (unsupported) feature that you can (optionally) enable in order to allow more than two of your users to be able to connect to WSE RemoteApp at exactly the same time (assuming that your server has the resources to support doing that). However, on very rare occasions, a Windows Update will disrupt that functionality and require that you install a newer version of the product in order to get things work again. This has nothing to do with your license (seeing as it is still completely valid for 10 users being able to access WSE RemoteApp), but you will need to have a valid “Updates and Support” option on your license in order to be able to install a newer release of the product (and/or receive any technical support for it).

To the best of my knowledge, this has only ever happened once with Essentials 2016, and that particular Windows Update was released way back in September of 2017. If for whatever reason, your server only just recently got that Windows Update installed (and it disrupted WSE RemoteApp 2016’s multiple simultaneous connections functionality), then you will need to install the latest release of the product in order to correct that issue. And, if the “Updates and Support” option on your WSE RemoteApp 2016 license is no longer valid, then you will need to purchase a license renewal for your existing 10 user license in order to be able to install the latest release of the product. License renewals (which renew the Updates and Support option on an existing valid license) are available for purchase in one year, two year, or lifetime timeframes.